High mechanical forces are necessary in order to be able to incorporate solids in liquid media. It is customary to employ dispersing agents in order to reduce these dispersion forces and in order to keep the total energy input into the system, which is necessary for deflocculating the solid particles and thus the time of dispersion also, as low as possible. These dispersing agents are surface-active substances of anionic, cationic or neutral structure. These substances are added in a small amount either directly to the solid or to the dispersion medium. Furthermore, it is known that even after complete deflocculation of the solid agglomerates into primary particles, re-agglomeration occurs after the dispersion process. Thus, the effort expended to produce a dispersion is partially or completely negated. The consequences of an unstable dispersion or of re-agglomeration are unwanted effects such as an increase of the viscosity in liquid systems, drift of colour tone and losses of gloss in lacquers and coatings, as well as a reduction of the mechanical strength of plastics.
There is a multiplicity of different substances which are used nowadays as dispersing agents for pigments and extenders. A review of the existing patent literature is given in EP 0 318 999 (page 2, lines 24-26). Apart from very simple, low molecular weight compounds such as lecithin, fatty acids and salts thereof, and alkylphenol ethoxylates for example, complex structures are also used as dispersing agents. In particular, these comprise amino- and amide-functional systems, which are widely used amongst dispersing agents. In GB 2 153 804 for example, amino- and amide-functional poly- and oligocopolymers based on polyamines and polycaprolactones are used for the dispersion of magnetic pigments. EP 0 713 894 describes the use of amino-functional polylactones for coatings and printing inks. Moreover, amine-functional polyacrylates (EP 0 311 157, U.S. Pat. No. 3,980,602) are used for the stabilisation of organic and inorganic pigments. Amine-functional polymers based on polyisocyanates constitute a further group (EP 0 159 678, EP 0 438 836).
Derivatives of phosphoric acid esters are also frequently used as dispersing agents. EP 0 417 490 (page 2, lines 23-43) gives a summary of the use of these substances, preferably as dispersing agents or for the pretreatment of pigments. The salts of acidic phosphoric acid esters are also described in this patent. Inorganic bases as well as mono- and diamines are listed as the basic salt formation components.
Whilst satisfactory stabilisation of pigments or solids can be achieved, many of these dispersing agents have an insufficient capacity for reducing the viscosity on the incorporation of pigments or of solid particles in binder vehicles and pigment concentrates. In the course of continuing efforts aimed at producing environmentally compatible systems, the necessity exists of reducing the amount of solvent as far as possible (e.g. high-solids and ultra-high solids lacquers), or of dispensing with solvent completely. In general, this leads to problems in production, since the viscosity is often too high on the incorporation or dispersion of solid particles. This is particularly relevant to the production of pigment concentrates, for which a degree of pigmentation which is as high as possible should be reached whilst at the same time keeping the proportion of binder vehicle or solvent low.
Pigment pastes only develop their fill capacity for use if they can be used as universally as possible, i.e. in many different binder vehicles which often differ considerably as regards their polarity. It is exactly this broad compatibility of pigment pastes which cannot be ensured by the dispersing agents used hitherto, so that the use of paste systems is significantly restricted. Apart from the use of pigment pastes in different binder vehicles, the miscibility of pastes with each other and in the binder vehicle without flocculation has to be ensured.
The aforementioned dispersing agents often only constitute partial solutions of this problem. On account of the multiplicity of inorganic and organic pigments and extenders which are used nowadays, satisfactory stabilisation of the solid particles to be dispersed is not ensured to an adequate extent by covering the surface in a manner which is stable as regards desorption. Agglomerates are thus formed, since the requisite, efficient steric hindrance is lacking.
The underlying object of the present invention is therefore to eliminate the aforementioned disadvantages of known dispersing agents, i.e. to develop dispersion additives which whilst ensuring good stabilisation of pigments or extenders reduce the viscosity of the milled material of lacquers, pastes or plastics formulations to such an extent that they can be processed at a high filling ratios. At the same time, particularly for pigment and extender pastes, a broad range of compatibility must be ensured so as to be able to use these in many different binder vehicles and coating materials. Moreover, it is necessary that the dispersion additives which are used according to the invention result in miscibility with each other of pastes, or of binder vehicles produced using these pastes, without flocculation.